Radio circuits



y 3 L, 1.. JONES ET AL 1,909,968

RADIO CIRCUITS Filed Oct. 25, 1929 3 Sheets-Sheet 1 i I 5 z I INVENTORS LESTER. L. JONES JACOB YOLLES l BY W W B 0 5m BIAS-T ATTORNEYS May 23, 1933. L. JONES ET AL 1,909,968

' RADIO CIRCUITS INVENTORS LESTER L.J'ONES In B JACOB YOLLES ATTORNEYS May 23," 19'33. l L JONES ET AL I I I RADIO-CIRCUITS Filed Oct. 25, 1929 3 Sheets-Sheet 3 FDAFDO QuzE.

0o. mwijmvE mi md il 11' lNVENTORs I LESTER L.JONE$ JACOB YOLLES BY WOW ATTORNEYS NOILVDIdITdWV Patented May 23, 1 9 33 UNITED sures LESTER L. JONES,- or ORADELL, .NEW JERSEY, ANnJAco'B YoLLEsoF BROOKLYN,

' .NEW YORK, ASSIGNORS TO TECHNIDYNE CORPORATION OF NEW YORK RADIO CIRCUIT Application filed October 25, 1929; semi No. 402.378.

This invention relates to radio circuits, and more particularly toLc1rcu1ts including vacuum tubes.

In some circuits including vacuum tubes the nature of the tube or the nature of the circuits cooperating therewith is such that the tube is characterized bv a constantapparent input capacitance. With such a circuit there is a tendency for the efficiency to fall off at the high end of the working range of frequency, owing to the decreased reactance of the tube input capacitance at high frequencies, there being, ordinarily, substantial impedance in the su ply circuit. One object of ourinvention is to overcome this tendency and to com--.

pensate for the loss in gain at the higher fre quencies so as to level the gain curve. For this purposewe connect in series with the input circuit of the tube an inductance which preferablyis made of suitable magnitude to series resonate with the apparent tube input capacitance at the high end of the frequency range. The series resonant decrease in impedance or short circuitcauses greatly 1ncreased current to flow, whlch 1ncreases the potential across either of the two series resonant reactances, and the resulting resonant rise in potential is impressed upon the-tube input electrodes, which areconnected across one of the series resonant reactances.

The manner in which an ordinary three electrodetube is given a constant apparent input capacitance may be, as in the caseof a detector tube, by shunting the output circuit with respect to radio frequency energy, so

that there is a negligible output impedance for such energy. Another example is a vacuuintube made reactionless by a special output circuit including'a regenerative feedback inductance and a degenerative feed forward resistance arranged in the manner described in a patent to Lester L. J ones, No. 1,713,132, issued May 14, 1929, and in his copending application, Ser. No. 397 ,632,filed Oct. 5, 1929. Also, a tube may be given a constant apparent input capacitance by reason of the construction of the tube itself, a common example be-' ing the screen grid vacuum tube, in which a fourth electrode prevents capacitive coupling between the control electrode and the anode of the'tube. The present invention is ge nerically applicable to all of the various foregoin and other similar arrangements.

' lVliile our invention is most conveniently applicable to the input circuit of a tube having a constantapparent-input capacitance it is not limited thereto for the inductance may be selected to series resonate with what value of input capacitance the tube has at the frequency at which resonance is desired. F orv example, our'inv'ention maybe applied to the input circuit of an automatically tuned tube, the inductance being, designed to series resonate with the small apparent input capacitance of the tube at the high frequency end'of the range. Also, when dealing with CORPORATION, OF NEW, YORK, N, Y., A

a tube which is automatically tuned ,over

tionthe'overall percentage increase in gainis not so great when applying-our invention to the succeeding tube because the gain in the" amplifier tube is apt to be reduced at high frequencies inasmuch as the series resonance of the input circuit of the succeeding tube will shunt or short circuit the output cir-- cuit of the first tube and reduce its impedg ance. Our invention more than makes up for this lossygiving a net gain, but the initial gain beinghi'gh, the relative or percentage increasein gain may not be very high. However, in'niany' instances the am plifiertubemay for other reasons be advan-' tageously' equi pped with an" output 'imped-' ance which is low relative to the optimum V impedance, and to such acircuit our inven t1on results in a high relat veor percentage increase in gain, because the reduction m gain in the amplifier tube is of little consequence, while the increase in potential applied to the second tube is relatively substantial, the initial gain not being very high. A more specific object of our invention, therefore, is to apply our series inductance to a. circuit including a tube following an amplifier tube having an output impedance which is less than the impedance value give ing maximum amplification- The amplifier may, for example, be a screen grid tube, the tube itself having a very high impedance which is difficult to match, or it may bean automatically tuned stage wherein, to obtain automatic tuning the output impedance is made 'less' than the optimum, particularly forhigh frequencies. I I

Automatic tuning is disclosed in the patentof Lester L. Jones, No. 1,678,287, issued June l2, 1928, which describes how, for this purpose, the output circuit of the tube'is made naturally resonant to a frequency lower than the working frequency range. The

output circuit is therefore characterized by decreasing impedance with increasing frequency, which causes decreasing apparent input capacitance for the tube, and this change in capacitance may be utilized for: automatic tuning of the input circuit to the received frequency. Obviously, the frequency range over which a single tube may be automatically tuned depends largely uponthe range of capacitance variation obtainable across theinput circuit of the tube.

'A further object of the present invention is to increase the available range of automatic tuning in such anautomatically tuned stage. I a

The automatically tuned stage is followed by another tube stage, and inmost cases by a stage in which the tube has a constant apparent input capacitance, as, for example, a

detector tube, or a reactionless link stage be,

tween cascaded automatically tuned amplifier ,1 stages, for with such a subsequent circuit the output circuit of the automatically tuned stage may readily be keptnaturally resonant to a constant frequency lower-than the work-.

ing frequency range. In accordance with the present invention an additional inductance is connected in series with the input circuit ofthe succeeding tube which series resonates with the apparent tube input ca.-

pacitance at high frequencies, short circuiting the output circuit of the automatically tuned stage, thereby greatly reducing the output impedance and therefore the gain in the tube itself, (though not in the complete stage),'and correspondingly decreasing the apparent inputcapacitance of the automatically tuned tube. This increases the total capacitance variation available for automatic tuning, and so increases the automatic tuning. f

To the accomplishment of the foregoing possible range of quency.

as hereinafter are more particularly de-.-

scribed in the specification and sought to be defined in the claims. The specification is accompanied by drawings in which:

Fig. 1 is a wiring diagram showing the applicationof our invention to a detector tube;

Fig. 2 isa wiring diagram showing the application ofour invention to a tube made reactionless by a special output circuit;

Fig. 3' is a wiring diagram showing the application ofour invention to the input circuit of an automatically tuned amplifier stage 7 V Fig. 4 is a wiring diagram showing the application of our invention to a screen grid tube;

Fig. 5 is a wiring diagram for an untuned screen grid cascade amplifier embodying our invention;

Fig. 6 is a fictitious circuit equivalent to one with a transformer having leakage flux;

Fig. 7' is a wiring diagram showing the ap plication of our invention to a tube follow ing an automatically tuned stage;

Fig. 8 is a graph showing the improvement in the gain curve resulting from the use of our invention;

Fig. 9 is a graph explanatory of additional advantages obtainable by the use of our invention; and V V Fig. 10 is a schematic wiring diagram for a radio receiving system of the pre-selector and automatically tuned type embodying our invention. I

Referring to Fig. 1 there is a detector tube 2 which, in the present case, is given an asymmetric characteristic in order to obtain rectification by means of a biassing battery 4. The output circuit of the detector'tube includes a filter stage 6 for separating the radio and modulation frequency components, this filter circuit including radio frequency bypass condensers S and 10 and a radio frequency choke 12. The output circuit of the tube 2 consequently has negligible impedance with respect to radio frequency energy, and the apparent tube input capacitance, represented by the dotted cOndenserQO, therefore has a small and constant value at radio fre- Modulated radio frequency energy is applied to the input circuit of the tube 2 by any suitable coupling means, exemplified in the present case by the transforinerQQ.

If the frequency of the carrier energy is varied from a relatively low'to a relatively high frequency the capacitance "is de-' creased in 'reactance, and thereis a tendency for the potential on the control elect-rode of the tube to diminisn, there being, ordinarily,

substantial,impedance in the supply circuit.

Now, in accordance "with our invention, an additional inductance 1sconnected in series order of 100,000ohms.

impedance which is low relative'to the opti; mum, the gain might be increased two-fold or three-fold. Our invention. may therefore most advantageously beapplied toamplifier circuits. in which the output impedance, isless than the optimum.

In the case of screen grid tubes. the anode to cathode resistance is very high, say of the, The external shunt capacitance on the plate is also high, being of the order of to 15. micro-microfarads, which tends to reduce the, effective external impedance. The optimum impedance should be at. least comparable with the tube impedance, and this. high impedance it is P122167 tically impossible to attain-without. utilizing an efficient tuned circuit. In the case of an untuned screen grid amplifier the. output circuit impedances are therefore less than the optimum value, andto. such an amplifier my invention may be applied with a substan-' tial overall increase ingain.

By way of illustration Fig. 5 of the draw-- ing shows an untuned cascade screen grid; amplifier. This amplifier comprises tubes 60, 62, and 64, followed by a detector tube 66. Tubes 60, 62', and 64 have constant apparent input capacitances because of the shielding effect of the screen grid employed in the tubes. Tube 66 has a constant" apparent input capacitance because of the negligible shunt impedance of the output filter section 68 for radio frequencies. The tubes are coupled by fixed transformers 70, 7 2, and 7 4, and these being untuned are low in impedance relative to the tube impedance, the screen grid tubes having a very high anode to cathode resistance.

Under these circumstances each of the tubes may especially advantageously be provided with additional series inductances, numbered 30, which in each case are'pr'eferably suitably dimensioned to series resonate with the apparent tube input capacitance at a desired frequency. If the transformers are naturally resonant to a frequency in the middle of the range a drop in amplification at the high frequencies may be avoided by the use of our invention, though a drop at low frequencies will still remain. If it is desired to obtain a substantially level amplification characteristic the transformers may be made naturally resonant to a frequency lower than the working frequency range. 'In such case there is decreasing amplification with in creasing frequency over the entire range owing to the diminishing output impedance value with increasingfrequency. Now, in accordance with our invention the inductance may be made to series resonate with the apparent input capacitance of the tubes at thehigh frequency end of the range, there by levelingout the gain curve; The percentage increase in gain obtained at the high frequencies is very substantial because for these frequencies the "output impedance of the transformers is quite, low, the natural res0.- nance frequency thereof being considerably departed from at the high frequencies.

In another aspect, the fact that the coupling impedance between the tubes should not be a very high impedance may be eX- plained because the resonant rise in potential obtained across either of the two series resonant reactances is caused by a large current flow, and in order to permit free circulation orgrowth of this large current the impedance across which the series resonant circuit is connected must itself not be too high.

It. will be observed that the input circuit of the. tube 60. is connected across a variometer 76., in series with an antenna circuit 7 8', which is; an effective capacitance, or in other words, that the input circuit of the tube is connected across an inductively tuned .circuit. This represents another type of circuit to which the present invention is especially advantageously.applicable, for when dealing with inductively tuned circuits the efliciency ofthe circuits falls off at the higher frequencies, owing to the greatly reduced value of inductance employed, for the resonant rise in a tuned circuit is greater in a so-called stiff circuit, having a large ratio of inductance to capacitance for a given frequency. This principle may, of course, be applied to a cascade tuned amplifier when the tuned circuits are inductively rather than capacitively tuned.

The antenna circuit 78 is not a true capacitance, the antenna lead-in being equivalent to a series inductance 80. This inductance remains fixed and its presence necessitates that the variable inductance 7 6 be made especially small at high frequencies, which aggravates the looseness of the coupling of tube 60 to the antenna circuit, and increases the importance of our invention. 1

At this point it may not be amiss topoint out one advantage in using bifilar or substantially unity coupling transformers as the coupling transformers 70, 72', and 7 4. Referring to Fig. 6, there is a tube 210, the output circuit of which is coupled to the input circult of a tube 212 by means of a transformer 2-14. This transformer is assumed to have leakage which is represented in the present case by an equivalent diagram including series inductances 216 and 218. The trans former is shunted by associated capacitance so that at high frequencies the coup-ling is weakened further than at low frequencies Our invention may be applied to circuits including transformers with less than unity coupling in order to overcome this difliculty. although certain troubles may arise which are subsequently pointed out, but unity coupling preferred in order toavoid the said troubles and the aggravated 'l 'ooseness' of coupling at high frequencies which is caused by stant apparent. input capacitance, represented by "he dot-tedcondenser 20, and it may,

0 1- for e: an1ple,he a detector tube, as 1n 1* 1g.

l, or a reactionlesslink tube, as inFig. 2, or

a screen grid tube, asin Fig. 4. Tube 82 is precededby an amplifier 8e'hav1ngan output transformer 86 ,wh1ch is naturally resonant in circuit to a frequency lower than thefrequency range orersrhich the stage is to be automatically: tuned. Frequenciesgin the workingfrequency range are therefore higher, and for them the output circuit of tube 84.;is effectively capacitive and characterized by a decreasing impedance with in creasing frequency,thereby causing decreas ing gain and decreasing alternat ng potential on the anode of, tube 84with increasing frequency, which in turn causes-a reducton 1n the apparent input capacitance of the tube, representedby the dotted yariablecondenser 88. Condenser 88 is automatically variable in the proper sense forautomatic tuning, and the inputtransformer 90-is selected to be naturally resonant in circuit with the variable capacitance 88 for the desired frequency range. I i y Obviously, the range of frequency to which such an automatically .tunedstage may be kept in tune depends largely upon the range of variation obtainable in the apparent input capacitance 88. In accordance with our invention an inductance is connected in series with the inputcircuit of the tube 82, and isso proportionedasto serieszresoe nate with the apparent input capacitanceQO ofthe tube 82at the high frequency endof the range.. This results not only ina gain in potential applied to the control electrode of tube82,but the series resonant shunt,

across transformer 86 greatly reduces the impedance thereof atthe-high frequency end of the range, thereby greatly reducing the alternating anode potential on tube 84, which in turn causes a reduction in the apparent input capacitance 88, thereby increasing the un le of capacitance available for automatic and so increasing the frequency the automatically tuned amplifier m In range of stage.

In Fig. 8 we have plotted two curves showing amplification a function of wave length; This amplificationds measured in terms of the ratio of the potential across the input circuit f thc'tube havingthe series inductance 30 to the potential across the input circuit of the preceding tube. For example, in Fig. 7 of the drawing the amplification would be measured by the ratio of the potential between the control electrode and cathode of ,tubef82'to the potential bethen departed from there is still some reso nant potentialrise. Itshould be observed that theimprovement indicated by curve B'does not include the gain due to the betterautomatictuning of tube 84 in Fig. 7 for the comparison is made between potentials existingbeyond the tuned input circuit of tube 8 4. The gain shown is therefore that obtainable by; the

useof series resonance in the inputcircuit ,of tube 82 whcnusmgia coupling means whichis not a very highnnpedance, for the resonance frequency of transformer 86 is considerably departed from at the; high frequencyend of the range. I t 1 An automatically tuned stagesuch as is illustrated in Fig. 7 preferably employsbifilar wound transformers, that is, the coupling transformers 86 and 90 are bifilar wound orotherwiseconstructed to have sub stantially unity coupling, for this, in additi on to maximum coupling,mal :es possible the obtention of a relatively smooth and gradually varying input capacitance curve,;,-in-

of inflectionpoints.

stead of an irregular curve having a number It may be desired to stillfurther. improve the gain at the high frequencyend ofathe range when usinga circuit such as :is illustrated in Fig. 7 or in fact, when using any circuit employing fixed coupling transformers which are bifilar wound or otherwise constructed to have substantially unity coupling Referring to Fig. 9, the dotted curve C; represents the apparent'input capacitance vvariationof a tubesuch as the tube 84 in Fig.

7 when using a bifilar output transformer such as the transformer 86, andwithout using the inductance, 30. A decreasing capacitance with decreasing frequency;as at the-point 92, is caused by an inductive output circuit, having decreasing impedance with decreasing frequency; Aninductive output'circuit-causes regeneration, and the region 92 therefore a regioirofregenera-v tive reaction. Increasing capacitancewith decreasing frequency, as at the point 94, is caused by increasing output impedance with decreasing frequency, indicating that the out:- put circuit is capacitive. A capacitive out,- put circuit causes degenerative reaction, and therefore theregion 94; is a region, of degenerativereaction. An inflectionpoint such as the'point 96 has Zero slope and represents a frequency at which the output circuit is neither capacitive nor inductive, but rather is resonant'or resistive, and at such a point there is neither regenerative or degenerative reaction. 7

When the inductance is added in the input circuit of tube 82 the input capacitance curveis changed from the simple dotted curve C to the more complex solid line curve D, which has an additional peak caused by the resonant shunt 30, 20. The region 96,

like the region 94, is degenerative. The inflection point 98, like the inflection point 96, is a point of neither regenerative nor degenerative reaction. The region 100, like the reg1on92, is regenerative in reaction. For automatic tuning of the input circuit of an amplifier tube there must be increasing.

capacitance with decreasing frequency, so that regions 94 or 96 may be utilized'for automatic tuning. By adjusting the constants of the circuits so as to locate the inflection point 98 at the high frequency. end

of the range the gain at that end of the range circuit may be so chosen that the inflection point 98 is at a frequency higher than the range. Automatic tuning will then take place over the portion 96 only of curve D, and there will be no regenerative reaction throughout the range, just as though no inductance 30 were employed.

In Fig. 10 we have illustrated a radio receiver embodyingvarious features of our invention. This receiver comprises an antenna circuit 102, the energy collected by which is fed to a selector 104 having variable circuit constants, after which the energy of selected frequency is amplified in a radio frequency amplifier 106,'having fixed circuit constants, the amplifier energy being detected in a suit able detector 108, from which the rectified energy may be fed to an audio frequency amplifier and a' reproducer in the conven tional manner. This general arrangement of pre-selection in tuned circuits followed 'by amplification in an amplifier having fixed circuit constants is set forth in a copending application of Lester L. Jones, Ser No.

205,934, filled July 15, 1927 ,while the particular form of radio frequency amplifier here set forth, which consists of a plurality of either single or multistage automatically tuned amplifiers separated byreactionless link stages is set forth in our copending application, Ser. No. 403,161, filed October 29, 1929. Y

Referring to the wiring diagram of Fig. 10, the selector 104'is followed by a reactionless link stage 110, which may be designed in accordance'with the teachings of the copending application Ser. No. 397,632, previously referred to in connection with Fig. 2, or may be a screen grid tube, as disclosed in our copending application Ser. No. 403,161, filed October 29, 1929, and which is designed to prevent reaction from the amplifier 106 upon the selector 104. The link stage 110 is followed by an automatically tuned amplifier 112. This may consist of one 'or more tubes or stages arranged in cascade and designed for automatic tuning over the entire frequency range, in accordance with the teachin s in the copending application Ser. No. 391,633, already referred to.

As is set forth in our copending application Ser. No. 403,161, supra, if further amplification is desired it is not feasible to cascade directly upon an automatically tuned amplifier suchlas the amplifier 112, another and similar automatically tuned amplifier, such as the amplifier 114, each being tuned over the full frequency range, but it is possible to do so provided the automatically tuned am plifiers 112 and 114 are linked by a stage, such as the link stage 116, characterized by a consections, in accordance'with the teachings of the copending application of Lester L. Jones,

Ser. No. 402,379, filed October 25, 1929.

In accordance with the present invention the inductance 30 is connected in series with the input circuit of tube 118, and is made of suitable magnitude to series resonate with the apparent tube input capacitancethereof. Transformers and 122 are preferably bifilar wound in order to prevent irregular in flection points in the reaction and capacitance curves ofthe circuits, and the sections of the transformers are dimensioned to be naturally resonant to a frequency higher than the frequency range in order to avoid inflection points which would be caused by high impedance due to resonance within the working frequency range. would be especially injurious when employing a series input inductance such as the inductance 30 because the successful operation of the series resonant shunt requires the flow of large currents which would be prevented Such resonance points by resonance and concomitant high impedance 1n the coupling transformer. The nductance 80 18 itself astatlcally wound in order to prevent magnetic coupling Wit 1 other pie-X output circuit. As before, the input and output transformers 128 and 130 are preferaloly bifilar wound, and they, as well as the series inductance 30, are astatically wound,

transformer 128 being wound, if necessary,

in four sections in order to prevent resonance within the working frequency range.

The automatically tuned stage 124 is in this case illustrated as having only a single stage; The input circuit thereof is provided with a series inductance 30, in g. 3 of the present application, inductance 30 seriesresonating with that value of apparent'input capacitance of the tube which it has at the high frequency end of the range, in order to boost the gain at that point. i

The automatically tuned amplifier 124 is followed by the detector stage 108, and this is characterized by constant apparent input capacitance by reason of the output circuit being shunted for radio frequencies by shunt condensers, as in the filter section 6. The detector stage 108 is similar to that set forth in Fig; 1 of the drawings, except thatthe' input transformer 132 and the series inductance 30 are shown to be astatically wound,

transformer 132 being wound in four-sections to prevent resonance within the working frequency range. a

By using the inductance 30 in the detector stage the tuning range of the amplifier stage 124 may be considerably broadened, as was previously explained in connection with Figs. 7 and 9 of the drawing. Ordinarily it is therefore not necessary to additionally use the inductance 30 in the input circuit of the automatically tuned stage, as is shown in the amplifier 124. However, it is perfectly feasible to employ both induetances in order to boost the gain at still higher frequencies,but

in such case the precaution must be observed of staggering or making somewhat different the resonance frequencies of the two series resonant circuits, for otherwise oscillation may be set up.

In general, it may be mentioned that the series inductance 30 should have small distributed capacitance, that'is, it should be substantially inductive. The reason for this is that the resonant rise in potential varies inversely as the decrement or directly as the so-called stiffness of the circuit, and this requires as large a ratio as possible of inductance to capacitance. The effective inductance of'aninductance shunted by a capacitance is increased, and therefore the ratio of the inductance 30 to the apparent input capacitance would be decreased bygcapaci 'tance in shunt with inductance 30. Also, if

the inductance consists of'a low inductance shunted by capacitance, instead of a high substantially pure inductance, the inductance value falls off rapidlyat the low frequency endv ofthe range, thereby spoiling the gain in that region.

The inductance 30 is made resonant with,

the apparent input capacitance 20 at the high :frequency end of the range not only because in most cases that is where the extra gain is needed,but also because it is only with this arrangement that improved gain may be obtained over the entire frequency range. If inductance '30 were made series resonant with capacitance 20 at the low frequency end of the range some gain would be obtained at low' frequencies, but at high frequencies inductance 30 would act as a choke and severe loss would result. When inductance 30 is made series resonant with capacitance 20 at thehighfrequency end: of the'range, at low frequencies inductance 30 is of reduced reactance, and not only does not diminish the pedance peaks at some frequencies'which will prevent the desiredcirculating current when using the series resonant shunt circuit. ,Of course, when using automatically tuned stages it is anyway desirable to have substantially unity coupling transformers in order to simplify the design of the automatically tuned stages. In general, it is desirable and simple to have transformers which have impedances which vary smoothly with frequency, and which do not have resonance points within the working frequency range. 1 i I i From the foregoing description it will be understood that our invention is applicable to almost any vacuum tube circuit, and very conveniently applicable to those in which the input'capaoitance of the tube is substantially" made reactionless by .a special output circuit, or .a screen grid tube- It will also be understood that our invention is, advantageously applicable to a cascade amplifier of the untuned type, of the automatically tuned type, and of the inductively tuned type. lNhen used with the automatically tuned type of amplifier the gain may be Very much increased at the high frequency ,end of the range by elimination of degeneration, and if desired, by the introduction ofregeneratio-n, at the high frequencies.

It will be apparent that while we have snown and described our invention in the preferr'er forms, many changes and modifications may be made in the circuits disclosed without departing from the spirit of the invention, defined in the following claims;

We claim: I I

1. In the operation of. an automatically tuned amplifier stage, the method of increasing the range of automatic tuning which includes shunting the output circuit of the automatically tuned stage by a series circuit of inductance and capacitance of proper relative magnitude to series resonate at the high frequency end of the range.

2. In the operation of an automatically tune-d amplified stage having an output circuit coupled to a succeeding input circuit by a substantially unity coupling, the method of reducing the damping in the input circuit of the automatically tuned stage at the high frequency end of the range which includes shunting the secondary of the output circuit by a series circuit of inductance and capacitance of proper relative magnitude to series resonate at the high frequency end of the range and adjusting the resulting inflection point in the inputcapacitance curve of the amplifier to be at the high frequency end of the frequency range.

3. A radio circuit comprising an electron emission tube, an output circuit therefor including aregenerative feed back inductance and a degenerative feed forward resistance arranged to prevent reaction through the tube, and an input circuit therefor compris ing coupling means and an additional inductance connected inseries therewith between the coupling means and the tube.

4:. A radio circuit comprising a screengrid electron emission tube, and an input circuit therefor comprising bifilar wound transformercoupling means and an additional in; ductance connected in series with the secondary thereof between the secondary and the control electrode of the tube.

5. A radio circuit for operation over a range of radio frequencies comprising an electron emission tube and an input circuit therefor comprising coupling means and an additional inductance connected in series between the coupling means and the following tube, said inductance being of suitable magnitude to series resonate with the apparent tube input capacitance at the high frequency end of the frequency range,

6. A radio detector circuit for operation over a range of freuency, comprising a detector tube and an input circuit'therefor comprising coupling means and an additional inductance connected in series between the coupling means and the following tube, said inductance being of suitable magnitude to series resonate with the apparent tube input capacitance of the detector tubeat the high fresuitable magnitude to series resonate with the apparent tube input capacitance at the high endof the frequency range.

i 8. A radio circuit for operation over a range of radio frequencies comprising a screen grid electron emission tube, and an input circuit therefor comprising coupling means and an additional inductance connected in series between the coupling means and the following tube, said inductance being of suitable magnitude to series resonate with the apparent input capacitance of the tube at the high end of the frequency ranger v 9. A radio circuit for operation over a range of radio frequencies comprising an electron emission tube, an input circuit therefor including coupling means and an'additional inductance arranged in series therewith between the coupling means and the tube, and an output circuit arranged to automatically tune the input circuit, the additional induc-' tance in the input circuit being of suitable magnitude to series resonate with the apparent tube input capacitance at the high end of the frequency range.

10. A radio circuit for operation over a range of radio frequencies comprising an amplifier tube having an output circuit the impedance of which is less than the optimum impedance for maximum amplification, a second vacuum tube, and an input circuit therefor comprising means coupled to the output circuit of the amplifier tube and an additional inductance connected in series between the coupling means and the second tube, said inductance being of suitable mag nitude to series resonate with the apparent tube input capacitance of the second tube at the high frequency end of the frequency range.

11. A radio circuit for operation over a mfig: radio i frequencies comprisingan amplifier tubehaving an'output circuit the impedance of'which is less than the optimum impedance for maximum amplification, a

: detector tube, andian input circuit therefor comprising means coupled to the output circuitof the amplifier tube and an additional inductance connected in series between the coupling nieans and the detector-tube, said inductance being of suitable magnitude to series resonate with the apparenttube input capacitance of the detectortube at ,;the high frequency end of the frequency range.

12. A radiocircuit for operation over a range of radiofrequenc'ies comprising an amplifier tube having an output circuit the impedanceof which is less than the optimum impedance for maximum amplification, another vacuum tube, an output'clrcuit therefor including a regenerative feed back 1nductance and a degenerative feed forwardresistance arranged to give thetube a substantially constant apparent input capacitance, and an input circuit therefor-comprising means coupled to the output circuit 9f the amplifier tube, and an additional inductance connected in series between the coupling means and the second tube,said induc- I tance being of suitable magnitude to-series' resonate with theapparent tube input capaci V tanceof the'second tube at the high frequency end of the frequency range.

- 13. A radio circuit for operation over a" range of frequency comprising an amplifier m'atically tunesrthe inputcircuit over the tube having an output circuit the impedance of which is less than the optimum impedance for maximum amplification, a screen grid tube, and an input circuit therefor comprising means coupled to the output circuit of the amplifier tube, and an additional inductance of suitable magnitude to series resonate with theapparenttube input capacitance of" the screen gridtubeat the high frequency end of the frequency range. i i

-314.'*A radio circuit for operation overa range 0f radio frequencies comprising an amplifier tube having input andoutputcir cuits'so arranged that the output circuit autofrequency range, a second vacuum tube, and an input'ici'rcuit therefor compris ng means coupledto the output circuit of the amplifier tube, and an additional inductance connected in seriesbetween the coupling means and the second tubeysaid inductance being of suitable magnitude to series resonate with the apparent t'ubeinput capacitance of the second tube at the highfrequency end of the frequency" 1 15L A radio circuit for operation over'a range ofradio frequencies comprising an amplifier tube having input and output circuits s o arranged that the output'circuit automatically tunes the input-circuit "over "thefrequ'ency range, a detector tube,"and

an input circuit'therefor comprising means coupledto the output circuit of the amplifier 1 tube, and an additional inductance connected"- in seriesbetween the coupling meansandthe' detector tube, said inductance being ofsuit-' able magnitude-to series resonate with the apparent'tube input capacitance of the detector tube at'the thefrequency range. 1

16.,A radio circuit for operation over a range of radio frequencies comprisingan amplifier tube having input and outputoircuits so arranged that the outputcirlcuit high frequency "end; of

automaticallytunes thefin'put circuit over the frequency range, a second vacuu m tube, an output circuit therefor includinga re generative feed back inductance and a degenerative feed forward resistance arranged to give the tubea substantially constant ap parent input capacitance, and an input 'cir-" cuit therefor comprising means cou led'to the output circuit of the amplifier tu e, and

an additional inductanceconnected in series between the coupling means and the second tube, said inductance being of suitable mag-- nltude to series'resonate with the apparent tube inputcapacitance of the second tubeat the high frequency end of the frequency:

range.

17 A radio circuit for operation overa' range of frequency comprising an amplifier to the output circuit'of' the amplifier tube, and an'additional inductance of suitable magnitude to series resonate with the '-ap-, parent tube input capacitanceof the screen" grid tube at the high frequency end of the frequency range. 18. A radio circuit for operation over "a range 'of' frequency comprising 'an' amplifier tube having input and output circuits solarrangedthat the output circuit automatically tunes'the input circuit over the frequency range, a secondvacuuintube characterized by a constantappar'ent input capacitance, and; an input circuit therefor comprising means coupled to the output'circuit of the amplifier tube; and an additional inductance of suit able magn'itudeto series resonate with the apparent tube input capacitance ofthe second tube at the high,frequency'end'ofthe frequency range, in order to increase the range of capacitance change 'and the range of automatic tuning-ofthe input ci-rcuit of the first tube. i

19. A radio circuit for tube having input'and output circuitsiso ar ranged that the output cireuitautomaticallyf tunes'the input circuit over the fr'equencyrange, a second'vacuum', tube characterized I operation over "a range of frequency comprising an amplifier- 

